Halogen-releasing bleach compositions are generally recognized as having greater oxidizing power than other bleaching agents such as peroxygen compositions. Bleaches which release hypochlorite or hypobromite ion are particularly effective, as is known in the art.
Because hypohalite-releasing bleaches are such effective oxidants, however, problems may arise during use. Fabric and dye damage may result from locally high concentrations of hypochlorite or hypobromite if the dry bleach is not diluted with wash water prior to introduction of fabrics or if undissolved bleach granules settle on fabrics subsequent to laundering. Additionally, chlorine and other halogen bleaches are incompatible with some laundry additives such as enzymes and optical brighteners, since strong oxidizing agents can render these additives ineffective.
Several solutions have been proposed to counter these problems. One proposed solution to the problem of enzyme degradation in particular is the introduction of a chlorine scavenger into a bleach composition in order to delay the release of chlorine into the wash water. In U.S. Pat. No. 3,893,954 to Tivin et al., for example, a hydroxyamine compound is added to an enzyme-containing detergent to react with residual chlorine. Another proposed solution to the problem of fabric damage caused by high chlorine concentration is the addition of diluents to the dry bleach which are admixed, compacted and granulated with the bleach itself. U.S. Pat. No. 4,309,299 to Rapisarda et al. shows, for example, the admixture and compaction of diluents such as succinates and citrates with chlorine bleaches to improve chlorine retention characteristics. Stabilizers such as potassium carbonate have also been used, as taught in U.S. Pat. No. 2,695,274 to MacMahon et al.
Another approach to solving the problems caused by excess hypochlorite in solution is encapsulation of the bleach. Encapsulation techniques are known for both peroxygen and chlorine bleaches. U.S. Pat. No. 4,126,573 to Johnson, for example, shows the encapsulation of a peroxyacid bleach with a water-soluble surfactant compound. Several patents teach the use of coatings derived from fatty acids, such as U.S. Pat. No. 4,327,151 to Mazzola, which discloses an encapsulated bleaching agent having an inner coating of a fatty acid and a microcrystalline wax, and an outer coating of a fatty acid and Pluronic surfactants, and U.S. Pat. No. 3,983,254 to Alterman, which shows a method of encapsulating bleaching agents with fatty acids and alkali metal salts of fatty acids. Other encapsulated bleaches are also known. For example, U.S. Pat. No. 4,279,764 to Brubaker shows encapsulation of a mixture of an organic nitrogen-containing halogen bleaching agent, an N-H containing compound, and a soluble inorganic hydratable salt. U.S. Pat. No. 3,036,013 to Jaszka teaches an encapsulated calcium hypochlorite bleach. While the inventions of these patents share the same characteristic of encapsulation, they vary as to temperature dependence, shelf stability, and most importantly, as to the timing of the bleach release.
In order to provide an effective timed-release bleach, not only must hypochlorite release into aqueous solution be delayed, but the timing for complete release into solution must also be controlled. That is, even where the solubility of the encapsulate coating is selected such that hypochlorite release is delayed, complete release must in addition be accomplished before the end of the wash cycle to avoid settling of bleach capsules on fabric. Such settling could cause fabric and dye damage. This problem has been found, for example, with some coated calcium hypochlorite bleaches. Elimination of the problem requires a coating with appropriate solubility characteristics and one which will not interact with the bleach granules in a way that is inhibitory to the dissolution process.
It is also desirable to provide a bleach that in addition to having superior timed-release characteristics, also has good storage life, is effective over a broad range of concentrations, and is also effective over a broad range of temperatures.